Solar Panel Lifespan and Degradation: What 25 Years Really Looks Like in a Hot Climate

Ask how long a solar panel lasts and you will usually hear twenty five years. That figure is a warranty term. It is not a date on which the panel stops working, and treating it as one leads to two opposite mistakes: owners who expect nothing to change until year twenty five, and owners who assume a panel in year twenty six is scrap.

What actually happens is slower and less dramatic. Output declines a little every year, and the rate of that decline, rather than any fixed lifespan, decides what the array delivers over its life. The rate varies with the product, the installation and the climate, and in hot climates the conditions that speed it up are present every day.

Lifespan and Degradation Are Different Questions

Lifespan is how long a module keeps producing safely and usefully. It usually ends for one of two reasons. Either output has fallen far enough that replacing the module pays, or a physical failure makes it unsafe: broken glass, a burnt junction box, insulation that no longer holds, a backsheet cracked through to the cells.

Degradation is the rate at which output falls while the module is still working. It is expressed as a percentage per year and it compounds into real money over a long life.

Design qualification does not settle either question. Modules are type approved to IEC 61215, which subjects samples of a design to accelerated stress: thermal cycling, damp heat, humidity freeze, UV exposure and mechanical load. Passing shows the design survives that sequence. The standard itself is clear that its results are not a quantitative prediction of module lifetime, which depends on design, environment and operating conditions. A certificate is a minimum entry ticket, not a forecast.

What the Field Data Says

The most widely cited figure comes from a review by Dirk Jordan and Sarah Kurtz at the US National Renewable Energy Laboratory, since renamed the National Laboratory of the Rockies. They assembled nearly 2,000 degradation rates measured on modules and systems over forty years of field testing and found a median of 0.5 percent per year.

A later compendium by the same group, drawing on over 11,000 rates, put the median for crystalline silicon at 0.5 to 0.6 percent per year, with means of 0.8 to 0.9 percent. A mean above the median tells you the distribution has a long tail: most systems degrade slowly, and a minority degrade much faster. The same work notes that hotter climates, and mounting arrangements that keep modules hot for long periods, may lead to higher degradation in some products, though not all, and that most modules decline in a fairly linear way.

The arithmetic shows why the spread matters more than the median. At 0.5 percent a year, a module loses about 12.5 percent of its output over twenty five years and still delivers roughly 87.5 percent. At 1 percent a year it delivers roughly 75 percent. At 2 percent it delivers roughly half. The median describes a well-made module installed well. Your array might not be that module.

The First Year Is Different

Many crystalline silicon modules lose a slice of output early, and the mechanisms are distinct from long-term ageing.

Light-induced degradation. In the first hours to days of sunlight, some cell types lose a little power as defects form in the silicon. Manufacturers have reduced this through changes to wafer doping and cell technology, but susceptibility still varies by product.

Light and elevated temperature induced degradation. A slower effect, seen in some high-efficiency cell types, that develops over months to years at operating temperature and may partly recover. Heat is part of its name for a reason.

This is why performance warranties allow a larger drop in year one than in later years, as our guide to solar PV warranties explains. The compendium also documents significant deviations between beginning-of-life measurements and nameplate rating, which matters to an owner: a module can arrive below its rating. A measured baseline beats a datasheet.

The Mechanisms That Take Output Away

Potential induced degradation (PID). In a long string, modules towards the ends can sit at a high voltage relative to their earthed frames. That voltage can drive ions through the glass and encapsulant towards the cells, degrading them. IEC distinguishes two forms, PID-shunting and PID-polarisation, and publishes test methods for detecting them in crystalline silicon modules in IEC TS 62804-1, revised in 2025. Heat and moisture accelerate PID. It often shows as a pattern along the string, with the modules nearest one end losing the most power. Caught early, some forms can be partly reversed; left alone, the loss deepens.

UV exposure and encapsulant browning. The encapsulant that bonds cells to glass can discolour under years of UV and heat, cutting the light that reaches the cells. Better encapsulant formulations have reduced it, but a high-UV site is where any weakness shows first.

Delamination and moisture ingress. The bonds between glass, encapsulant, cells and backsheet can fail, letting moisture in to corrode cell metallisation and interconnects. Daily thermal cycling works at these bonds constantly.

Cell cracks and hot spots. Microcracks start in transport, in handling and when people walk on modules. Thermal cycling grows them until parts of a cell stop contributing. A cell that cannot carry the string's current is driven into reverse and heats up, and a hot spot can scorch the backsheet and, at worst, start a fire. Localised shade and bird droppings do the same thing to healthy cells.

Bypass diode failure. Bypass diodes in the junction box let current pass around a shaded or damaged cell group. A diode that fails short takes its cell group out of production permanently. One that fails open removes the protection, so the next hot spot has nowhere to go. Junction boxes run hot in sun, which does diodes no favours.

Soiling, which is not degradation. Dust is a loss, often a large one, but it is reversible. It is regularly mistaken for degradation, and an owner who measures a dirty array will conclude the modules have aged when they only need cleaning. Clean before you measure. Our guide to solar panel maintenance in dusty climates covers cleaning without damaging the glass.

The mechanisms that take output away from a working module. Soiling is included because it is so often mistaken for degradation. Source: MIMAH engineering practice.

Heat Costs You Twice

Heat reduces output in two separate ways, and confusing them leads to the wrong diagnosis.

The temperature coefficient is reversible. Silicon cells produce less power as they get hotter. The datasheet states the effect as a percentage per degree Celsius, applied to how far the cells run above 25 °C, and on a hot afternoon the loss is substantial. When the module cools, the power returns. Nothing has been damaged. This is the loss described in our article on solar efficiency loss in extreme heat, and it is a design input, not a fault.

Accelerated ageing is permanent. Most of the degradation mechanisms above are chemical or mechanical processes that run faster at higher temperature: encapsulant discolouration, corrosion, PID, and the fatigue of solder bonds under large daily temperature swings. A module that spends its days hotter ages faster, and that loss does not come back when the sun goes down.

Hot climates add more. UV dose is high, dust abrades glass, and the swing between a desert afternoon and a clear night cycles every bond in the module every day. The 110 sites MIMAH installed across Sudan during 2025 operate in exactly these conditions.

Design can mitigate much of it.

Let the modules breathe. Mounting with an air gap behind the modules, on raised racks rather than flush against a hot roof, lowers operating temperature, and lower temperature helps both the reversible and the permanent loss.

Choose modules on evidence. Look for test results beyond the IEC 61215 minimum, PID testing to IEC TS 62804-1, a datasheet temperature coefficient that suits the climate, and a construction suited to heat and UV. Glass-glass modules are often chosen for harsh sites for their resistance to moisture and backsheet damage.

Design the string voltage and earthing for PID. Follow the module and inverter manufacturers' guidance on system voltage, earthing arrangement and any PID mitigation they specify.

Handle modules like glass. Vertical transport, no standing on modules, and no dropping them from the back of a truck. Microcracks created on installation day grow for the life of the plant.

Two different losses from the same heat. Only one of them comes back at night. Source: MIMAH engineering practice.

How to Measure Degradation

Degradation is only visible against a reference, which is why the commissioning record matters so much. Four methods, used together, give an honest picture.

Performance ratio trending. A monitoring system that measures plane-of-array irradiance and module temperature can calculate performance ratio continuously. Over several years, with soiling and outages accounted for, the slope of that trend is the system's degradation rate. Energy alone will not show it, because weather varies more from year to year than the modules do.

IV curves against the commissioning baseline. A string IV curve traced by the same method as at handover, translated to standard test conditions, shows how much peak power each string has lost and whether the curve's shape has changed. This is the comparison that makes a baseline worth recording, and our guide to solar PV commissioning covers how to get one.

Thermography. An infrared survey in strong sunlight finds hot spots, bypass diodes carrying current, and PID patterns across strings. The procedure for PV plants is set out in IEC TS 62446-3. It finds faults quickly across a large array but does not measure power.

Electroluminescence imaging. Passing current through a module in the dark makes the cells emit light that a suitable camera can see. Cracks and inactive areas show up dark, often before they produce any thermal signature. It is the method that proves cracking, and the evidence most likely to support a claim for cell damage.

For a formal claim, a sample of modules can be removed and flash tested in a laboratory to measure power at standard test conditions accurately.

Four measurement methods, each seeing something the others miss. All of them depend on a reference taken at commissioning. Source: MIMAH engineering practice.

What the Performance Warranty Protects

Performance warranties are now commonly linear: a first-year allowance, then a fixed maximum annual decline down to a guaranteed floor at the end of the term. It pays out only when measured output falls below that line, and proving it is the owner's job, with measurements corrected for irradiance, temperature and soiling.

A module degrading at twice the median rate may still sit above its warranty line for years. That shortfall is lost revenue with no claim attached. The warranty protects against a defective product. It does not protect against a product that is merely worse than average, nor against damage the manufacturer attributes to installation or handling, which is typically excluded. The difference between those cases is usually settled by evidence gathered long before anyone thought about a claim, and several of the installation faults that cause it are covered in why solar systems fail early.

What Twenty Five Years Looks Like

A well-made module, mounted with airflow, handled properly, kept clean and watched by a monitoring system, loses a modest fraction of its output over twenty five years and carries on producing afterwards. Replacement becomes a commercial decision about whether newer modules would earn back their cost, not a deadline.

A poorly chosen or poorly installed module in the same climate can lose several times as much, and the owner may not notice until the loss is large, because nobody recorded where it started.

MIMAH's renewable energy team designs and installs solar systems for hot, dusty sites and carries out performance audits on existing arrays. If your system's output has drifted and you want to know whether it is soiling, faults or degradation, get in touch.